The rates generally increased with age, with 41.5 percent of teens having obesity by 16-19 years of age. Researchers used National Health and Nutrition Examination Survey data to calculate age- and sex-specific body mass index, with updated obesity classifications, from height and weight measurements taken during physical exams. This approach revealed more nuanced trends, study authors said, including rates for severe obesity, more specific age subgroups, and added long-term context. Of particular concern, authors said, were continued racial and ethnic disparities--especially at the most extreme weight categories. White and Asian children, for example, showed significantly lower rates of obesity than Hispanic and black children. Examining short-term trends as well as long-term, researchers also found a sharp increase in obesity since 2015-16 among children ages 2 to 5, especially boys. Girls 16 to 19 years old also had a notable jump in overweight rates, from 36 percent to 48 percent.

Study authors said that despite intense clinical and public health focus on obesity and weight-related behaviors in the past decade, results suggest these efforts have yet been able to counteract environmental forces that fuel excess weight gain in children, at least on a national scale. They call for more widely disseminated resources and additional research into the factors contributing to childhood obesity.